The present invention relates to an imaging process involving hardening of the photosensitive microcapsules in the border area of an imaging web.
Photosensitive materials have been used in many applications including imaging systems. For example, commonly assigned U.S. Pat. Nos. 4,399,209 and 4,440,846 disclose imaging systems wherein the imaging sheet comprises a support with a layer of microcapsules on the surface thereof. The microcapsules have an internal phase of a photohardenable photosensitive composition and a color former. The microcapsules are image-wise exposed to actinic radiation and ruptured so that the color former reacts with a developer material to produce an image.
In the transfer imaging system of U.S. Pat. No. 4,399,209, the imaging sheet is contacted with a receiver sheet comprising a developer sheet having a support with a layer of developer material on the surface thereof prior to microcapsule rupture. In the self-contained imaging system of U.S. Pat. No. 4,440,846, the imaging sheet has developer material codeposited with the microcapsules on the surface thereof.
The imaging sheet of the aforementioned imaging systems is commonly in the form of a web and the receiver sheets are in the form of single sheets. Because the imaging web is typically slightly wider than the width of the receiver sheets placed thereon, and because the receiver sheets are placed on the imaging web with gaps existing between the ends of neighboring receiver sheets so that registration is practical, each receiver sheet is "framed" by an uncovered portion of the imaging web. Upon passage of the imaging web with receiver sheets thereon through the nip between two pressure rollers to rupture the microcapsules for image development, the internal phase of the ruptured microcapsules on the uncovered portion of the imaging web collects on the surface of the pressure rollers. In addition to contaminating the rollers, the internal phase on the rollers can be transferred to other surfaces such as to other areas of the development apparatus or to the backs of subsequent receiver sheets passing through the pressure rollers. Receiver sheets having soiled backs are undesirable Also, cleaning the contaminated pressure rollers and related fixtures is time consuming and expensive.
Also, another problem thought to be unrelated, exists with pressure development of the aforementioned imaging web. An imaging web having a support of a polymeric film cannot be transported successfully through high pressure nip rollers because the imaging web will often deform.
U.S. Pat. No. 4,073,968 teaches a method of desensitization of a color developer sheet in areas which are usually not used for recording. To make the desensitized areas, the method involves coating a photocurable compound onto a layer of microencapsulated color former coated on paper, curing the compound, and coating the outer surface of the compound with a layer of developer material. By this method, the layer of color former and the layer of developer material are physically separated by the cured film to prevent color formation. A pressure is then applied to the assembly to form a color. In the desensitized areas, a color reaction does not occur. Because the microcapsule internal phase of color former in solvent can still be released during microcapsule rupture and collect on the surface of the pressure rollers, the method of U.S. Pat. No. 4,073,968 does not overcome the aforementioned contaminated pressure roller problem.
Thus, a need exists in the art for an imaging process and apparatus useful therein in which the uncovered portions of an imaging web do not contaminate the pressure rollers during pressure development.